Test Runner: Omit results files when too many failures. This will cause the test shards to be re-tried due to an invalid result. The goal is to retry flaky configs where whole shards fail. Bug: angleproject:6075 Change-Id: I76d0f08da29ffc4bcad7f282f7be38618c384bce Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2982500 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>